Gas analysis apparatus with proportioning means



Jan. 9, 1968 H. STUBEN 3,362,228

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A Jnven/or: 1&4 1442M United States Patent 3,362,228 GAS ANALYSISAPPARATUS WITH PROPORTIONING MEANS Hans Stiiben, Moorrege, KreisPinneberg, Holstein, Germany, assignor to H. Maihak Aktiengesellschaft,Hamburg, Germany, a corporation of Germany Filed Apr. 21, 1964, Ser. No.361,372 Claims priority, application Germany, Apr. 27, 1963,

M 56,630; July 10, 1963, M 57,440

7 Claims. (Cl. 73422) ABSTRACT OF THE DISCLOSURE A gas analysisapparatus comprises a piston slide valve which includes a pistonreciprocating in a complementary bore of a casing. The piston has atleast one recess which constitutes proportioning means. The casing hasinlet means and outlet means for gas to be analyzed and leading into andfrom, respectively, the bore of the casing. Additional inlet means andoutlet means for scavenging gas and leading into and from, respectively,the bore of the casing. The respective inlet and outlet means are spacedapart along the axis of the piston and the recess of the lattercoincides with the respective inlet and outlet means in the dead centerpositions of the piston during its reciprocation.

The present invention relates to a gas analysis apparatus withproportioning means in order that gases may be perfectly examinedanalytically also with higher concentrations than hitherto.

A known gas analysis apparatus, particularly for the determination oflow traces of hydrogen sulphide in gases of any kind and in air,operates according to the following principle: a narrow paper stripsaturated with a reagent which reacts to the particular gas, for examplehydrogen sulphide, and is stained under the influence of the gas more orless depending on the concentration of the gas, is moved at constantspeed successively through a comparison chamber and through a measuringchamber. The comparison chamber contains air, whereas a constant volumeof the gas to be analyzed is fed to the measuring chamber. The reagentpaper strip in both chambers is radiated by one common lamp. The paperbrightness acts on two light-sensitive elements. The first of the twoelements receives the light from the white paper strip in the comparisonchamber, while the light emitted by the more or less blackened paperinside the measuring chamher is directed towards the second of thelight-sensitive elements. The resulting differential current isproportional to the gas content, for example to the content of hydrogensulphide, of the gas to be analyzed and is measured by means of ameasuring instrument.

Such a gas analysis apparatus has a normal measuring range of 0 tomilligrams of hydrogen sulphide per standard cubic metre (mg. H S/Nm.with a flow rate of measuring gas of 100 emi /min. A four-fold range maybe achieved by reducing the gas flow rate to 50 cm. /min. and bydoubling the paper transport speed. Such conditions occur in tracemeasurements, for hydrogen sulphide for example, when contaminations areto be determined in a cleaned gas. High concentrations, however, are nolonger measurable because the quantity to be measured exceeds themeasuring range of the analysis apparatus. Such cases occur particularlywhen measuring H 8 in uncleaned gases when the concentrations of theuncleaned gas to be measured may exceed the measuring range of theanalysis apparatus for example by the factor 1000 and more.

In such cases it has hitherto been usual to add a measuring gas volumecompatible with the measuring range of the analysis apparatus to ametered volume of air, inert gas or other gas not interfering with theanalysis.

For proportioning or making gas mixtures it is known to usereciprocating pumps with two pistons of diflcrent diameters whichmoreover may have dilferent lengths of stroke and also different strokecycles per time unit. Perfect proportioning is however no longer ensuredif the mixing ratio exceeds a certain amount, for example 1:100, becauseowing to the arrangement of the necessary valves the detrimental spaceof the small proportioning piston becomes too large related to thestroke volume.

Another known proportioning device operates with a mechanicallyrotatable cock in which the bore of the plug is used as proportioningvolume. The cock body is provided with two bores disposed at angles ofto each other, the plug of the cock being provided with only one passagebore the size of which is adapted to the proportioning volume. Afterrotation by 90 the gas delivered into the bore of the cock plug throughone bore in the cock body is blown out of the plug bore by the gas to beadded and both gas volumes are combined and conducted to the analysisapparatus. Also this device has a limited proportioning capacity only,because the bore of the cock plug may not be selected too large in viewof the sealing requirementsthere must be sufficient overlapping betweenthe boreswhile at the same time also a certain mininum value must bereached if proper filling is still to be ensured during the few angulardegrees where the bores of the plug and of the cock body face each otheras the plug is turned. Another drawback appears in the course of timebecause scores readily develop on the continually turned cock plug whichmay result in leakage and consequent falsification of the proportioningvolume.

Moreover, the proportioning of low gas volumes easily creates the riskof a delay in indication because a current cannot form in the pipingfrom the sampling point to the proportioning device. For this purpose aT was installed upstream the proportioning device to allow a certainvolume of the gas to be analyzed continuously to flow out. Although suchan arrangement eliminates the delay caused by a long sampling line, yetthe volume of the connecting line between the T and the proportioningmeans is still large in relation to the small proportioning volume thuscausing a noticeable undesired delay in the indication.

It is one object of the present invention to provide a gas analysisapparatus with proportioning means which overcomes the drawbacksmentioned above.

It is another object of the present invention to provide a gas analysisapparatus with proportioning means which includes a piston slide havingat least one recess and reciprocating in a casing to be used forproportioning the gas, which by means of its recess or recesses providesfor the delivery of the gas to be examined from the gas sampling lineinto the proportioning means, when the piston slide valve has reachedone of its two dead center positions and for conveying the gas to beanalyzed by means of scavenging gas out of the proportioning means intothe measuring chamber of the gas analysis apparatus, when the pistonslide has reached the other of its two dead center positions.

It is still another object of the present invention to provide a gasanalysis apparatus with proportioning means, wherein the piston slideitself is used for proportioning and is provided with a recess asproportioning chamber in its center for this purpose. Annular groovesare provided in the casing at both ends of the piston slide travel atthe location of the proportioning chamber. The gas to be analyzed(measuring gas) flows through one of the annular grooves of the casing,while scavenging gas or air continuously flows at constant speed throughthe other of the annular grooves. During its stroke the piston slidecarries a predetermined volume of measuring gas in its proportioningchamber from one annular groove to the other annular groove from wherethe measuring gas is delivered to the measuring chamber of the gasanalysis apparatus. This embodiment is suitable for proportioningrelatively small volumes of up to 1.5 mm.

It is yet another object of the present invention to provide a gasanalysis apparatus with proportioning means, wherein the piston slidemerely serves for controlling a proportioning device, the proportioningchamber of which consists of an exchangeable tube mounted on the outsideof the casing. The piston slide is provided with several controllingedges, for example with three grooves for controlling the various gasways. One groove controls the entry of the scavenging gas into theproportioning tube, the second groove controls the entry of themeasuring gas into the proportioning tube, and the third groove controlsthe exit of the measuring gas from the proportioning tube. Thisembodiment is well suited for proportioning relatively highproportioning volumes of up to cm.

The gas analysis apparatus with the proportioning means designed inaccordance with the present invention offers the advantage that theproportioning means are easy to manufacture. Piston, casing andproportioning tube are preferably made of the same hardened material,for example stainless steel, so that these parts will not be attacked bythe gas to be measured, for example hydrogen sulphide. Furthermore, thepiston slide ensures a good overlapping between the recess or recessesin the psiton and the openings in the casing serving as gas inlets andoutlets thus maintaining a satisfactory sealing. Furthermore there is apossibility of wide variation in the proportioning volume by appropriateselection of the piston diameter, the size of the proportioning chamber,the size of the proportioning tube, and of the number of strokes perunit of time.

Furthermore there is no delay in indication because in the firstembodiment of the proportioning means the gas to be analyzed andproportioned continuously flows through one of the annular grooves inthe casing and the proportioning volume defined by the proportioningchamber in the piston is immediately carried along by the How ofscavenging gas upon entry into the other annular groove leading to themeasuring chamber of the gas analysis apparatus. Finally, owing to thelow speed of movement there is enough time available for filling theproportioning chamber When the piston slide valve reaches its deadcenter position. In the second embodiment of the proportioning means theflow conditions are even more favorable for the formation of theproportioning chamber proper as a tube of small inside diameter ensuresa satisfactory blowing out of the metered measuring gas by thescavenging gas.

Advantageously the piston slide of the proportioning means is alsodriven by the clockwork for transporting the reagent paper strip of themeasuring device, so that the piston slide valve will positively bemoved in synchronism with the transport. But it is also possible toactuate the proportioning means by an electromagnet with pull-backspring, thereby making possible to provide for an intermittentproportioning with a program suited for the particular application ofthe gas analysis apparatus.

With these and other objects in view which will become apparent in thefollowing detailed description, the present invention will be clearlyunderstood in connection with the accompanying drawings, in which:

FIGURE 1 is an elevation, partly in section, of the proportioning meanswith the piston slide and the proportioning chamber in the supply lineof the gas to be examined;

FIG. 2 is an elevation, partly in section, of the proportioning meanswith the piston slide and the proportioning chamber in central position;

FIG. 3 is an elevation, partly in section, of the proportioning meanswith the piston slide and the proportioning chamber in the measuringline;

FIG. 4 is a sectional view of the piston slide with an annular grooveserving as proportioning chamber;

FIG. 5 is a sectional view of the piston slide with a bore serving asproportioning chamber;

FIG. 6 is a sectional view of the piston slide with milled faces;

FIG. 7 is an elevation of a piston slide valve with an adjustableproportioning chamber;

FIG. 8 is an elevation of the proportioning means, as driven by anelectromagnet;

FIGS. 9 and 10 are diagrams of a gas analysis apparatus withproportioning means;

FIG. 11 is an elevation of a proportioning device with a proportioningtube fitted to the outside of the casing with the piston slide shown inthe position in which the proportioning tube fills with measuring gas;and

FIG. 12 is an elevation of the proportioning device of FIG. 11 with thepiston slide shown in the position in which the metered volume ofmeasuring gas is pressed out of the proportioning tube by the scavenginggas.

Referring now to the drawings, and in particular to FIG. 1, theapparatus comprises a casing 1 provided with a cylindrical bore 2 inwhich a piston 3 is reciprocated by a crank drive 4. The piston 3 isprovided in its center With a groove 5 extending all around the piston 3and forming the proportioning chamber or proportioning volume. Thereciprocating motion of the piston 3 defines a certain path for theproportioning chamber 5. Annular grooves 6 and 7 are provided in thecasing 1 at both ends of the path. The gas to be analyzed andproportioned flows through an inlet sleeve 8 into the annular groove 6,passes through the latter and leaves the groove 6 through the outletsleeve 9. Air, for example, is fed in through an inlet sleeve 10 and,after flowing through the annular groove 7, leaves again through theoutlet sleeve 11 from where it is conducted to the measuring chamber.

Referring now again to the drawings, and in particular to FIG. 2, piston3 has reached its center position after rotation of the crank drive 4,the proportioning chamber 5 now being located between the two annulargrooves 6 and 7. The proportioning chamber 5 has taken out of theannular groove 6 the volume of gas to be analyzed, which volume ispredetermined by the size of the proportioning chamber 5. Theproportioning chamber 5 is now sealed by the overlapping casing 1. Asthe piston 3 is moved towards the annular groove 7, the volume of gasenclosed in the proportioning chamber 5 is also conveyed thereto. Thegas to be analyzed continues to flow through the inlet sleeve 8, theannular groove 6 and the outlet sleeve 9, while at the same time aircontinues to flow to the measuring chamber through the inlet sleeve 10,the annular groove 7 and the outlet sleeve 11.

As indicated in FIG. 3, piston 3 has reached the other dead centerposition of the piston path after further 1'0- tation of the crank drive4 by 90. The volume of the gas to be analyzed enclosed in theproportioning chamber 5 has now reached the annular groove 7 where it istaken along by the air flow and conveyed to the measuring chamber of thegas analysis apparatus. The gas to be analyzed continues to flow throughthe inlet sleeve 8, the annular groove 6 and the outlet sleeve 9.

As the crank drive 4 is further rotated by the piston 3 again reachesits starting point, so that the proportioning chamber 5 is again locatedin the annular groove 6, as shown in FIG. 1. The air contained in theproportioning chamber is displaced by the gas to be analyzed flowingthrough the inlet sleeve 8 and the annular groove 6 to the outlet sleeve9, so that the proportioning chamber 5 again fills with measuring gas.Since the gas to be analyzed continuously flows through theproportioning means there will always be fresh gas at the samplingpoint, that is in the annular groove 6. A delay in indication is thusexcluded.

FIGS. 4, 5 and 6 are sectional views of difierent embodiments of theproportioning chamber 5. FIG. 4 shows an annular groove 12 the depth andwidth of which may be varied. FIG. 5 shows the piston 3 with a bore 13as proportioning chamber, the diameter of which may be varied withincertain limits. FIG. 6 shows a proportioning chamber formed by milledrecesses 14 on the piston 3. In all these three cases also the outsidediameter of the piston 3 may be varied for changing the size of theproportioning chamber.

FIG. 7 discloses a piston having a proportioning chamber adjustable insize. For this purpose the piston 3' is composed of two parts. At theend, remote from the crank drive 4, piston 3' carries a centering shaft15 with a threaded pin 16 having a bush 17 screwed thereon. The width ofthe annular groove and consequently the size of the proportioningchamber 5' and the proportioning volume may be varied by shifting thebush 17 on the centering shaft 15. The adjustment of the bush 17 issecured by means of a counter nut 18.

FIG. 8 indicates how the crank drive may be replaced, for example, by anelectromagnet 19. In the attracted state of the magnet 19, as shown, theproportioning chamber 5 is located at the level of the annular groove 7,whereas in the currentless state the spring 20 causes the piston 3 withthe proportioning chamber 5 to move in front of the annular groove 6 itbeing of no importance whether the proportioning chamber 5 is filled inthe attracted state or in the currentless state of the magnet.

The operation of a gas analysis apparatus with proportioning means willnow be described with reference to FIG. 9. The supply line 21 of the gasto be analyzed includes a pressure regulator 22 which provides for thepressure in the proportioning means not to exceed a certain value. It isthus prevented that the gas to be examined overflows in theproportioning means from annular groove 6 to annular groove 7.Substantially, there is a pressure of about 50 to 100 mm. column ofwater in the measuring line 23 and it is therefore desirable to maintainthe same pressure or a slightly lower pressure in the annular groove 6of the gas to be analyzed. The regulator 22 also comprises a capillary25 arranged in the discharge line 24 of the gas to be analyzed. Thewater column 26 indicates the pressure existing in the annular groove 6of the gas to be analyzed. There must always be the same pressure in theannular groove 6, so that the volume of gas removed by the proportioningchamber 5 will always remain equal. If this is not ensured, the contentsof the proportioning chamber 5 will increase or decrease depending onthe pressure in the gas line. Operation therefore takes place at aconstant overpressure, for example 80 mm. column of water, against theatmosphere.

The volume of gas to be analyzed transported by the proportioningchamber 5 into the annular groove 7 is conveyed by the air used asscavenging gas through the measuring line 23 to the measuring chamber27. In the measuring chamber 27 the measuring gas acts in known manneron a reagent paper strip 28, which is moved forward by feed means 29,for example a clockwork motor, intermittently, for example with 12 stepsfor each field at a speed of one step per minute. The air is dischargedfrom the measuring chamber 27 through the line 30 which is preferablyprovided with another capillary 31 before it is led into the outgoingair shaft in order not to let the pressure in the annular groove 7 fallbelow the pressure of the annular groove 6 and especially in order toprevent a short-circuit across the outgoing air shaft between the gasdischarge lines 24 and 30. The other reference characters refer to thesame parts as in the FIGS. 1 to 3.

FIG. shows the same scheme of a gas analysis apparatus withproportioning means as FIG. 9, the only modification being that thepressure regulator 22 is replaced by a capillary 31' in the supply line21 of the gas to be analyzed. The capillary 31 provides for a pressurein the proportioning means which is approximately equal to the pressurein the line 30 and does not exceed the pressure in the annular groove 7.An approximately constant pressure is thus ensured in the annular groove6. The other reference characters refer to the same parts as in FIG. 9.

With reference to FIG. 11, the casing 1 is provided with a cylindricalbore 2 in which the control piston 6 is tightly fitted and isreciprocated by the crank drive 4 Piston 3 is provided with threerecesses for controlling the various gas ways. Scavenging gas, forexample air, enters through the inlet sleeve 32 into the casing 1 of thepiston slide 3 passes into the recess 33 of the piston 3 leaves thecasing 1 through the outlet sleeve 34 and is conveyed to the measuringchamber 35 of the gas analysis apparatus. The branch-01f line 36 ofoutlet sleeve 34 and/or measuring chamber 35 is sealed by the piston 3.The measuring gas to be analyzed enters through the inlet sleeve 37 intothe casing 1, flows around the recess 38 in the piston 3 and passesthrough outlet sleeve 39 into the proportioning tube 40 which it fillswith measuring gas and re-enters through inlet sleeve 41 into the casing1, passes into the recess 42 in the piston 3 and escapes through outletsleeve 43 to the atomsphere.

FIG. 12 shows the crank drive rotated by out of the position shown inFIG. 11. The outlet sleeve 34 for the scavenging gas is now closed bythe piston 3 The scavenging gas now flows through inlet sleeve 32,recess 33 of the piston 3 outlet sleeve 39, into the proportioning tube40, pushes the measuring gas ahead of itself through inlet sleeve 41,recess 42 and outlet sleeve 36 to the measuring chamber 35 of the gasanalysis apparatus in which the measuring gas acts in known manner onthe reagent paper 44. The measuring gas which continues to flow throughthe proportioning means passes through the inlet sleeve 37 into therecess 38 of the piston 3 from where it unobstructedly escapes throughthe outlet sleeve 43 into the atmosphere.

After rotation of the crank drive 4 by another 180 the position shown inFIG. 11 is reached again. The scavenging gas in the proportioning tube40 is displaced by the measuring gas and the proportioning tube 40 againfills with measuring gas. The quantity of the proportioning volume isfixed by the length of the exchangeable tube. The proportioning volumemay amount up to 10 cm. and more.

While I have disclosed several embodiments of the present invention, itis to be understood that these embodiments are given by example only andnot in a limiting sense, the scope of the present invention beingdetermined by the objects and the claims.

What I claim is:

1. A gas analysis apparatus including proportioning means comprising apiston slide including a piston having at least one recess constitutingproportioning means,

a casing having a cylindrical bore of a diameter complementary to thatof said piston,

said piston reciprocating in said bore of said casing and serving toproportion the gas to be analyzed,

first inlet means for gas to be analyzed leading into said bore,

first outlet means for said gas extending from said bore,

second inlet means for scavenging gas leading into said bore,

second outlet means for said scavenging gas extending from said bore,

said first inlet means and said first outlet means being spaced apartalong the axis of said piston from said second inlet means and saidsecond outlet means, said piston during its reciprocation assumingrespective end positions and moving said gas to beanalyzed accumulatedin said proportioning means from said first inlet means to said secondinlet means, a measuring apparatus communicating with said second outletmeans, and said casing having annular grooves spaced apart along thelongitudinal axis of said piston and surrounding said piston forcontinuous communication between said first inlet means with said firstoutlet means and between said second inlet means and said second outletmeans, respectively. 2. The gas analysis apparatus, as set forth inclaim 1, wherein said recess in said piston defines an annular chamber,

and said annular chamber communicates with said respective inlet andoutlet means in the end positions of said piston. 3. The gas analysisapparatus, as set forth in claim 1, wherein said recess in said pistondefines a crosswise disposed bore, and said bore communicates with saidrespective inlet and outlet means in the end positions of said piston.4. The gas analysis apparatus, as set forth in claim 1, wherein saidrecess in said piston defines lateral cut outs, and said lateral cutouts communicate with said respective inlet and outlet means in the endpositions of said piston. 5. The gas analysis apparatus, as set forth inclaim 1, wherein said piston comprises two parts movable relative toeach other and defining adjustably said proportioning means. 6. The gasanalysis apparatus, as set forth in claim 1, wherein said measuringapparatus includes a reagent paper strip, and includes drive means forsaid piston and for the transport of said reagent paper strip. 7. Thegas analysis apparatus, as set forth in claim 6, wherein said drivemeans for said piston comprises an electromagnet and a pull-back springoperatively connected with said electro-magnet for the return movementof said piston.

References Cited UNITED STATES PATENTS 2,622,015 12/1952 Cooper et al23-255 2,846,121 8/1958 Ronnebeck 73-421.5 X 3,076,697 2/1963 Miller etal 23254 MORRIS O. WOLK, Primary Examiner.

R. E. SERWIN, Assistant Examiner.

